# How do we know the size of the universe?

• B
I constantly hear facts like, if an atom was enlarged to the size of the solar system, a string would be the size of a tree. But how are we able to calculate the size of the universe if it may be infinite? Is it just the observable universe?

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Orodruin
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Is it just the observable universe?
Yes. This will typically be what someone referring to "the size of the Universe" means.

Lunct
Yes. This will typically be what someone referring to "the size of the Universe" means.
Thanks

stefan r
I constantly hear facts like, if an atom was enlarged to the size of the solar system, a string would be the size of a tree. But how are we able to calculate the size of the universe if it may be infinite? Is it just the observable universe?
Plank length 1.6 * 10-35, hydrogen atom 2.5 * 10-11 difference is around 1024
Hydrogen atom 2.5 * 10-11, solar system 1013 difference is around 1024

if an atom was enlarged to the size of the solar system, a string would be around the size of a atom

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Plank length 1.6 * 10-35, hydrogen atom 2.5 * 10-11 difference is around 1024
Hydrogen atom 2.5 * 10-11, solar system 1013 difference is around 1024
I watched a documentary and it said tree, I admit I was a bit surprised - I thought they would be much smaller. An atom makes so much more sense.
Thanks for the clarification.

Plank length 1.6 * 10-35, hydrogen atom 2.5 * 10-11 difference is around 1024
Hydrogen atom 2.5 * 10-11, solar system 1013 difference is around 1024
That would mean if you would enlarge an atom to the size of the observable universe, the planck length would be equivalent to the size of around two hundred pinheads.
May be wrong

stefan r
That would mean if you would enlarge an atom to the size of the observable universe, the planck length would be equivalent to the size of around two hundred pinheads.
May be wrong
better to find a mid point IMO.
8.7×1026 m
1.62×10−35 m
Maybe a fog particle or width of human hair.
You could also break it up into 3 units of 1020. plank length:diameter of nucleus, nucleus:width of New Jersey, New Jersey: diameter observable universe.
Orders_of_magnitude_(length)

"200 pin heads" could be a 10X20 pile or 200 in a row.